The present invention relates to inkjet printer, and particularly although not exclusively to a method and apparatus for servicing a pen when mounted in a printer.
lnkjet printing mechanisms may be used in a variety of different products, such as plotters, facsimile machines and inkjet printers, collectively called in the following as printers, to print images using a colorant, referred to generally herein as xe2x80x9cink.xe2x80x9d These inkjet printing mechanisms use inkjet cartridges, often called xe2x80x9cpens,xe2x80x9d to shoot drops of ink onto a page or sheet of print media. Some inkjet print mechanisms carry an ink cartridge with an entire supply of ink back and forth across the sheet. Other inkjet print mechanisms, known as xe2x80x9coff-axisxe2x80x9d systems, propel only a small ink supply with the printhead carriage across the printzone, and store the main ink supply in a stationary reservoir, which is located xe2x80x9coff-axisxe2x80x9d from the path of printhead travel. Typically, a flexible conduit or tubing is used to convey the ink from the off-axis main reservoir to the printhead cartridge. In multi-color cartridges, several printheads and reservoirs are combined into a single unit, with each reservoir/printhead combination for a given color also being referred to herein as a xe2x80x9cpen.xe2x80x9d
Each pen has a printhead that includes very small nozzles through which the ink drops are fired. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewleft-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor.
To print an image, the printhead is scanned back and forth across a printzone above the sheet, with the pen shooting drops of ink as it moves. By selectively energizing the resistors as the printhead moves across the sheet, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text). The nozzles are typically arranged in one or more linear arrays. If more than one, the two linear arrays are located side-by-side on the printhead, parallel to one another, and substantially perpendicular to the scanning direction. Thus, the length of the nozzle arrays defines a print swath or band.
That is, if all the nozzles of one array were continually fired as the printhead made one complete traverse through the printzone, a band or swath of ink would appear on the sheet. The height of this band is known as the xe2x80x9cswath heightxe2x80x9d of the pen, the maximum pattern of ink which can be laid down in a single pass.
The orifice plate of the printhead, tends to pick up contaminants, such as paper dust, and the like, during the printing process. Such contaminants adhere to the orifice plate either because of the presence of ink on the printhead, or because of electrostatic charges. In addition, excess dried ink can accumulate around the printhead. The accumulation of either ink or other contaminants can impair the quality of the output by interfering with the proper application of ink to the printing medium. In addition, if colour pens are used, each printhead may have different nozzles which each expel different colours. If ink accumulates on the orifice plate, mixing of different coloured inks (cross-contamination) can result during use. If colours are mixed on the orifice plate, the quality of the resulting printed product can be affected. For these reasons, it is desirable to clear the printhead orifice plate of such contaminants and ink on a routine basis to prevent the build up thereof. Furthermore, the nozzles of an ink-jet printer can clog, particularly if the pens are left uncapped in an office environment.
In an off-axis pen, life goal is on the order of 40 times greater than a conventional non off-axis system, e.g. the printhead cartridges available in DesignJet(copyright) 75xc2x0 C. color printers, produced by Hewlett-Packard Company, of Palo Alto, Calif., the present assignee. Living longer and firing more drops of ink means that there are greater probability that the printer print quality degrade and/or deviate along life. This requires finding better ways to keep functional and stable our printheads during long periods and large volumes of ink fired and moreover more accurate ways of detecting the end of life of this pens.
In U.S. Pat. No. 5,455,608 it is described how a printer may adjusts servicing of the pen based on the result of the current drop detection step only. Before starting a plot these printers perform a drop detection on all the pens to detect if there are any non-firing nozzles (xe2x80x9cnozzles outxe2x80x9d). If a single nozzle out is detected in a pen, the printer triggers a so called automatic recovery servicing process for servicing the malfunctioning pen to recover the malfunctioning nozzle(s).
This process includes a sequence of 3 nozzle servicing or clearing procedures of increasing severity which are performed in sequence so long as some of the nozzles of the printhead fail to fire ink drops pursuant to ink firing pulses provided to the printhead or until all of the procedures have been performed.
At the end of each of these procedures a new drop detection is performed on the pen, to verify if the pen is fully recovered. If, according to the current result of the drop detection, it is not, the subsequent servicing procedure is performed. If, at the end of the 3 functions, the pen is still not fully recovered (i.e. at least one nozzles is still out) the user is reported to replace the pen or to disable the nozzle check. One big drawback of this system when implemented, e.g. as in DesignJet (copyright) 750 C printers, is that if the printer is not able to fully recover the failing nozzles or there are some unstable nozzles, the system will remain in this recovery servicing mode until the decease of the printhead, being forced, by the permanent nozzle out, to run this process at the beginning of each plot. This usually leads to either an unacceptable loss of throughput and printer productivity (because the printer stops and waits for an answer, the automatic recovery process is very time consuming, and causes a big loss of ink particularly when running the priming functions) or to excessive printhead replace or continue messages that users disable nozzle check via front panel, causing throughput losses.
In the DesignJet(copyright) 750 C printers an end of life message is presented to the user when at least one nozzles results was not successfully recovered by the recovery procedure. This solution presents the following disadvantages:
Printhead transient problems will count as failures. An example of this could be a paper crash that produces a transient problem but the system is able to clear the nozzles after some plots or a few recovery cycles;
Stopping printing at this point and asking for replacement is against the unattendedness and networkability objective of the printer;
In addition, users may not have immediately available a new printhead to replace the failing one.
HP Professional Series 2000C printers produced by Hewlett-Packard Company, of Palo Alto, Calif. use the change of printhead thermal characteristics to detect when the standpipe fills of air, and thus is approaching end of life. But this method takes into account only the failure mode associated with air in the pen, but not issues related to nozzle health, which are usually more generic. To encompass the rest of failure modes, Rogue uses also drop counting for End of Life xe2x80x9cdetectionxe2x80x9d: when pen has fired a certain number of drops, printer advises user to get a new printhead. Main drawback of drop counting is that when the printer warns the user, the printhead may be working still well and a replacement would not be advisable.
With reference to the present application with the term plot it is identified any kind and size of printed output of the printer, seen by the printer as a single job. The plot could then identifies a CDA image or a graphic image like a photo or any other kind of print.
The specific embodiments and methods according to the present invention aim to improve the detectability of the end of life of a pen mounted in a printer device having a plurality of ink nozzles ejecting ink.
According to an aspect of the present invention it is provided a method for determining the end of life of a pen comprising a printhead having a plurality of nozzles, to be used in a printer for printing plots, comprising a drop detector and a servicing area, where servicing functions are executed to recover malfunctioning nozzles, the method comprising the following steps performing a drop detection on the printhead to check if any of the nozzles of the printhead are malfunctioning; storing the result of the more recent drop detection, together with the results of the previous drop detections to keep a history of the health status of each nozzle; by evaluating the history of the health status of each of the nozzles of the printhead, deciding whether or not to mark the pen as an end of life pen.
This method taking into account the health history of the nozzles helps to take a decision to replace the pen based on the first sporadic bad behavior of the pen that can be recovered quickly.
Preferably the method comprise the step of marking the pen as an end of life pen if the total number of malfunctioning nozzles is more than a first predetermined threshold.
This further helps to not consider in the decision to change the pen small or minor defects, such as one or two nozzles presenting malfunctioning during long periods.
Viewing another aspect of the present invention there is also provided an inkjet printer for placing droplets of ink on a medium comprising a pen comprising a printhead with a plurality of nozzles for ejecting droplets of ink, a droplet detector for identifying the nozzles of the printhead which currently present some malfunction in ejecting droplets of ink, said printer comprising a first memory means which contains for each nozzle the history of the malfunctions as identified by previous droplet detection, said history being used by the printer to identify the end of life of the pen.